Multi frequency mass spring oscillators

ABSTRACT

A multi frequency signal generator employing a cantilever beam comb wherein each beam has a different natural vibration frequency. The beams are selectively coupled through capacitive pickups to frequency modulate a high frequency oscillator. The modulated oscillator frequency is passed through a frequency discriminator, and the amplified output of the discriminator supplies the signal generator output and also is applied to a magnetic drive circuit for sustaining the selected beam in vibration at its natural frequency.

United States Patent [1 1 [111 3,742,387 Davis [451 June 26, 1973 [54] MULT] FREQUENCY MASS SPRING 2,901,936 9/1959 Scherer et a1 84/D1G. 21

()SCILLATORS 3,659,230 4/1972 Tanaka et al. 331/116 M X Inventor: Manfred Davis, 5958 Delafield Avenue, New York, N.Y. 104-71 Filed: Dec. 8, 1971 Appl. No.: 205,873

US. Cl 331/156, 84/D1G. 21, 310/25, 318/128, 331/179, 331/182 Int. Cl. 1103b 5/30 Field of Search 331/116 M, 156, 179, 331/182; 310/25; 318/128; 84/D1G. 21

References Cited UNITED STATES PATENTS 12/1942 Lovell 84/D1G. 21

MAGNETIC 3. DRIVER SENSOR SELECTOR 'i" i 9 OSCILLATOR FREQUENCY DlSCRlllglNAl'oR VOLTAGE EFMP EswR k Primary Examiner-Roy Lake Assistant Examiner--Siegfried H. Grimm 4 Claims, 2 Drawing Figures POWER AMPLIFIER BUFFER +0 OUTPUT AMPLIFIER Patented June 26, 1973 3,742,387

FIGURE 1.

come

MAGNETIC 3. DRIVE R SENSOR],H\\ SELECTOR i" 9 FREQUENCY OSOLLATOR fmscm rgmma COMP FELESSOR FIGURE 2.

MULTI FREQUENCY MASS SPRING OSCILLATORS SUMMARY made to achieve a high degree of frequency stability and accuracy at a very low cost. Many cantilever beams can be located side by side, as in a comb configuration, and individually adjusted to specific vibrational frequencies. A vibrating mode can be established for each beam by using an electromagnet with pole pieces large enough to influence all the beams.

FIG. 1 shows the mechanical embodiment of the invention. The associated electronic package is described schematically in block form in FIG. 2.

With reference to HO. 1: The cantilever beam comb (hereafter referred to as the comb) l is made from a magnetic high temper spring steel. The natural frequency of each of the beams is determined by its length and moment of inertia. Both of these parameters can be easily adjusted. The comb can also be made from a material with a low. rate of thermal expansion and in the event such materials are non-magnetic small magnetic pads can be welded to the end of each beam. Such a configuration provides for better frequency stability with respect to temperature changes. The comb is fastened to a brass inertial block 2 against which the beams can react. The block is also used as a clamp to hold all the parts of the mechanism together. An alternating magnetic field is generated by coil 5 and the laminated iron pole pieces 3. An electric current through coil 5 will cause the beams to be pulled towards the pole pieces. If the frequency of the current corresponds to the resonant frequency of one or more of the beams, the beams will vibrate at those frequencies. A direct current must also be present in the coil, the magnitude of which must approximate the peak value of the alternating current. If not, the beams will be pulled towards the pole pieces twice for each complete cycle of current, thus preventing vibrations from building up.

A thin phenolic plate 4 is installed between the pole pieces and the comb l. Conductive lands 7 are bonded to the phenolic plate 4 as shown. The lands fan apart and form the contacts of a selector switch. A common land 6 and a sliding contactor 8 comprise the rest of the selector switch. A push button configuration can also be used. Each of the lands form a variable capacitor with its corresponding beam. As a beam moves towards the land, the capacity increases. As the beam moves away from the land, the capacity decreases. The variation in capacity is used to alter the frequency of a high frequency oscillator MHz typical).

FlG. 2 shows the entire multi-frequency mass spring oscillator system. The high frequency oscillator 9 increases its frequency as the beam moves away from the pole pieces and decreases its frequency as the beam moves towards the pole pieces. This deviation is detected by the frequency discriminator 10 whose center frequency is adjusted to match the center frequency of the oscillator which therefore produces a voltage proportional to the beam position. This voltage is amplitied in the signal amplifier 11. The output of the signal amplifier 11 is fed into the driver amplifier 12 which operates into the electromagnet coil 5. If the phasing is correct and the gain of the amplifier is high enough, a feedback condition will be established which will sustain the vibration of the selected beam. The output of the signal amplifier can be connected to a buffer amplifier 13 before being led to the output terminal to provide better isolation and more output power.

A compression circuit 14 is used in the signal amplifier to provide a fast start-up of vibrations. When the vibrations are at a low level, the gain of the amplifier is high. When the level of vibrations builds up, the gain of the amplifier is automatically reduced by the compression circuit until a stable vibration level is reached. Effective compression can be achieved by using diodes back-to-back in the AC. negative feedback line of the voltage amplifier. Many other suitable amplitude compression circuits can be found in the technical literature. The invention is unique in that it causes the sustained vibration of a cantilever beam by use of a high frequency sensor and a feedback amplifier. Existing mass spring oscillators employ symmetrical vibrational modes, such as a tuning fork or a floating beam. Symmetrically vibrating systems cannot be coupled without energy transfer across the connecting nodev The cantilever beam comb, however, enjoys high isolation between the vibrating beams and, consequently, a small package can be used for'many frequencies. A high order of frequencies stability can be achieved at a low cost. Frequency stability can be increased by mounting the comb in an evacuated glass chamber. This prevents corrosion and increases the efficiency of the vibrations by eliminating the viscous drag in air. Further stability can be achieved by providing a constant temperature environment for the comb. Many vibrating beams can be constructed on a single comb, which is useful in the construction of cheap musical instruments. The device can be used to produce both an audible tone and an electrical signal at a desired frequency.

What is claimed is:

l. A device for generating electrical signals and audible tones of constant frequency comprising a cantilever beam comb, made of a material of high modulus of elasticity and made in such a manner as to render the tips of each beam magnetic, mounted to an innertial block and acted upon by a magnetic field produced by an electromagnet, a multi-element capacitance probe, one element corresponding to each beam of the comb, mounted in proximity to the beams for detecting the motion of the beams, a selector switch which allows electrical contact to be made to any of the elements of the capacitance probe, an electronic module containing an R.F. oscillator which operates in conjunction with the selected probe element to produce a frequency which varies as the corresponding beam of the comb moves, a frequency discriminator with center frequency corresponding to the center frequency of the R.F. oscillator which converts the frequency of the oscillator into a driving signal for a power amplifier and electromagnet, a voltage amplifier and compression circuit which is connected between the frequency discriminator and power amplifier providing voltage dependent gain such that when the vibration level of the selected beam is small the gain of the amplifier is high and as the vibration level of the beam increases the gain of the amplifier decreases, and a buffer amplifier which for thecantilever beam comb, and in the event that such material is non-magnetic, having small magnetic pads attached to the end of each of the cantilever beams in proximity to the electromagnet.

4. A device as described in claim 1 which in order to reduce cost at some compromise of frequency stability has the cantilever beam made entirely out of magnetic spring steel. 

1. A device for generating electrical signals and audible tones of constant frequency comprising a cantilever beam comb, made of a material of high modulus of elasticity and made in such a manner as to render the tips of each beam magnetic, mounted to an innertial block and acted upon by a magnetic field produced by an electromagnet, a multi-element capacitance probe, one element corresponding to each beam of the comb, mounted in proximity to the beams for detecting the motion of the beams, a selector switch which allows electrical contact to be made to any of the elements of the capacitance probe, an electronic module containing an R.F. oscillator which operates in conjunction with the selected probe element to produce a frequency which varies as the corresponding beam of the comb moves, a frequency discriminator with center frequency corresponding to the center frequency of the R.F. oscillator which converts the frequency of the oscillator into a driving signal for a power amplifier and electromagnet, a voltage amplifier and compression circuit which is connected between the frequency discriminator and power amplifier providing voltage dependent gain such that when the vibration level of the selected beam is small the gain of the amplifier is high and as the vibration level of the beam increases the gain of the amplifier decreases, and a buffer amplifier which provides a low output impedance for the connection of a load.
 2. A device As described in claim 1 which has increased frequency stability, wherein the cantilever beam comb and capacitance probe are contained in a constant temperature enclosure.
 3. A device as described in claim 2 which has further improvement in frequency stability by the use of materials which have a low coefficient of thermal expansion for the cantilever beam comb, and in the event that such material is non-magnetic, having small magnetic pads attached to the end of each of the cantilever beams in proximity to the electromagnet.
 4. A device as described in claim 1 which in order to reduce cost at some compromise of frequency stability has the cantilever beam made entirely out of magnetic spring steel. 